Many medical procedures require precise positioning of an instrument internal to a patient. For example, interventional instruments, such as needles or catheters, are used to obtain tissue samples (e.g., biopsies), to aspirate cysts or other objects, to deliver medication or other fluids directly into an artery or vein, etc. within or internal to a patient's body. Various devices and techniques have been tried to aid a clinician in the proper placement of the instrument.
For example, one technique utilizes a wire which is temporarily disposed in the lumen of a needle as the needle was inserted into a patient. A number of electromagnetic sensors are positioned around the patient to sense the proximity of the wire. Using triangulation techniques, the orientation and position of the needle may thus be estimated. The technique, however, is quite complicated and requires complex and expensive equipment which is limited in use to needle location estimation.
It is now common practice to use real-time ultrasound imaging to aid in the proper placement of the instrument. In such procedures the ultrasound transducer can be positioned along either the longitudinal axis of the instrument, often referred to as an in-plane technique (referring to the instrument being disposed longitudinally in the image plane of the ultrasound transducer), or transverse thereto, often referred to as an out-of-plane technique (referring to the instrument being disposed transverse or orthogonal to the image plane of the ultrasound transducer). For example, an instrument guide may be used to provide relative positioning of an instrument (e.g., a needle) and an ultrasound transducer so as to facilitate in-plane or out-of-plane techniques.
Regardless of whether an out-of-plane or in-plane technique is used, it is often very difficult to identify the instrument within a real-time ultrasound image. For example, instruments such as needles and catheters are relatively small and thus difficult to capture and display in an ultrasound image. The smooth surface of many instruments, such as needles and catheters, and their angle of insertion are often such that the instruments do not appear (or do not clearly appear) in an ultrasound image. Moreover, various structure and features within the object being imaged may obscure the instrument, or portions thereof. Even where a portion of the instrument is captured and displayed in an ultrasound image it is often difficult for a clinician to readily identify the instrument within the displayed image. However, various tissue (e.g., veins and arteries) are often disposed in close proximity and thus it is important to be able to precisely identify where the instrument is located. For example, it is often critical to accurately determine where the tip of a needle is so that procedures, such as obtaining tissue samples or medicine delivery, are not performed with an unintended target.
Accordingly, clinicians may employ alternative or supplemental techniques to identify the instrument within the image. For example, the clinician can “jiggle” the instrument to cause tissue or other internal structure to move, whereby this movement can be seen in the resulting image. Inferences can be drawn from the visible movement by the clinician as to where the tip of the instrument is presently located.
A variation on the foregoing technique is to utilize a device to induce vibration to the instrument. For example, a vibratory device may be applied to the external portion of a needle during a procedure and a Doppler image mode utilized by the ultrasound imaging system to provide artifacts in a resulting ultrasound image. However, the vibratory device is somewhat cumbersome and difficult to utilize in combination with needle insertion. Moreover, the technique results in somewhat imprecise depiction of the needle position because the color Doppler image modes used to display the needle vibration artifacts are generally of relatively low resolution which, particularly when combined with the vibration of the needle.
Other techniques have also been utilized in various attempts to provide information regarding the position of an instrument. For example, gradations or other markings may be added to the instrument itself for reference when determining its position. A needle may be provided with gradations along its shaft (e.g., 1 cm graduated markings), such that the number of gradations passing into a patient may be counted for a determination of the depth of insertion of the needle into the patient. Unfortunately, the lighting and other ambient conditions present during a procedure may not be conducive to an accurate count of such gradations. Moreover, a clinician performing a procedure is often unable to view the needle for sufficient periods of time to accurately count the passing of all gradations. For example, the clinician's view may be diverted periodically to the patient, to view other equipment, etc.
Still other techniques modify the instrument to provide facets or other perturbations upon a surface of the instrument in order to increase echogenicity of the instrument. For example, to facilitate reflection of an ultrasound signal the surface of a needle may be provided with a number of facets. An ultrasound system may thus provide an image of the needle, even with the needle is inserted at relatively acute angles, due to the facets causing ultrasound signals to be reflected toward the ultrasound transducer. Such facets have not, however, been found particularly effective in identifying particular portions of the needle, such as the tip. Moreover, the presence of the facets upon the surface of the needle affects the use of the needle, such as by causing insertion resistance, patient discomfort, etc.
A technique for determining the present position of the tip of the instrument is to insert dye or other contrast agent and observe visible changes within the resulting image. However, such a technique is often undesirable due to risks associated with injecting such media into a patient and the complexity added to the procedure associated with the use and delivery of such contras agents. Another technique for determining where the tip of the instrument is located is to modify the instrument itself (e.g., attach sensors thereto, provide visible markings thereon, and/or the like). Such techniques, however, are often undesirable due to the expense and complexity added to the procedure associated with the use of such special purpose instruments.
Another technique for determining the present position of the tip of the instrument utilizes a very small transducer disposed upon the end of a wire. The wire is inserted into the lumen of a needle so as to place the transducer at the tip. The transducer is activated during insertion of the needle to radiate ultrasound signals. A transducer of an ultrasound system receives the signals radiated by the transducer and image processing by the ultrasound system interprets these signals as a highly reflective point in the imaged volume. Thus the position of the tip may appear in the generated ultrasound image. However, the very small transducer and its associated control circuitry is relatively expensive and of use only for such procedures. Moreover, the procedure must be altered to include insertion and removal of the small transducer assembly within the needle.
From the above, it can be appreciated that when using the techniques discussed above the clinician must often guess where the tip of the instrument is and, based on this “best guess” estimation, perform the desired procedure. Alternatively, the instrument and/or the procedure may be adapted to facilitate more accurate determinations of instrument position. However, these adaptations introduce undesired complexity, risk, and cost to the procedure.